JVEsoft has a component suite for Delphi Firemonkey on IOS that contains support for three large advertising SDKs. The three are Chartboost, Appflood, and Revmob. Of coarse it also supports iAd and Admob but you are probably better off using a combination of all 5 than just sticking with one. JVEsoft has deployed a bunch of games to the App store so all of the components are tried and true and have seen use though the App store. If you do use these third party SDK ad components you should have your app download a configuration file from your server frequently that will allow you to enable and disable whichever ad networks you need. This will keep you from having to republish your app when you want to switch ad providers. The suite of components is commercial and there is no trial but I have purchased them and they come with source. They do not compile to Android so if you are building a cross platform app you will need to either modify them or IFDEF them only for IOS.
Take a look at the JVEsoft component suite and check out the help file.